U.S. Pat. No. 4,885,565, U.S. Pat. No. 5,638,060, U.S. Pat. No. 5,977,867, US2002/0075135 describe touch-operated apparatus having tactile feedback for a user when touched. In U.S. Pat. No. 4,885,565 an actuator is provided for imparting motion to the CRT when the actuator is energised to provide tactile feedback. In U.S. Pat. No. 5,638,060, a voltage is applied to a piezo-electric element which forms a switch to vibrate the element to apply a reaction force to a user's finger. In U.S. Pat. No. 5,977,867, a tactile feedback unit generates a mechanical vibration sensed by the user when the touch screen is touched with a finger or a pointer. The amplitude, vibration frequency and pulse length of the mechanical vibration are controlled, with the pulse width being long enough to be felt but short enough to terminate before the next key touch. US2002/0075135 describes the use of a second transducer to provide a pulse in the form of transient spike to simulate a button click.
WO 2008/045694 A1 of Immersion Corporation discloses a haptic effect device including a housing and a touchscreen coupled to the housing through a suspension. An actuator is coupled to the touchscreen. The suspension is tuned so that when the actuator generates first vibrations at a first frequency, the first vibrations are substantially isolated from the housing and are applied to the touchscreen to simulate a mechanical button. Further, when the actuator generates second vibrations at a second frequency, the second vibrations are substantially passed through to the housing to create a vibratory alert.
Other touch sensitive devices are described in US 2001/006006, US 2007/080951, US 2009/181724, US 2007/080951, US 2009/181724, WO 2008/151863, US 2009/189873, US 2009/267892, US 2008/100568, US 2007/024593, WO 2009/074826, JP 2009/245105 and US 2007/236450.